The present invention relates to imaging members. More particularly, the present invention relates to electrostatographic image transfer devices or imaging members comprising a transparent conductive layer of an evaporated metal halide. Electrostatographic image transfer devices are capable of having an image formed thereon which can be developed and transferred to a receiver such as a sheet of paper.
In electrophotography, an electrophotographic plate containing a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging its surface. The plate is then exposed to a pattern of activating electromagnetic radiation such as light. The radiation selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the electrophotographic plate to a support such as paper. This imaging process may be repeated many times with reusable photoconductive insulating layers.
An electrophotographic imaging member may be provided in a number of forms. For example, the imaging member may be a homogeneous layer of a single material such as vitreous selenium or it may be a composite layer containing a photoconductor and another material. One type of composite imaging member comprises a layer of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. U.S. Pat. No. 4,265,990 discloses a layered photoreceptor having separate photogenerating and charge transport layers. The photogenerating layer is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer.
As more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, degradation of image quality was encountered during extended cycling. Moreover, complex, highly sophisticated duplicating and printing systems operating at very high speeds have placed stringent requirements including narrow operating limits on photoreceptors. For example, the numerous layers found in many modern photoconductive imaging members must be highly flexible, adhere well to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits to provide excellent toner images over many thousands of cycles. One type of multilayered photoreceptor that has been employed as a belt in electrophotographic imaging systems comprises a substrate, a conductive layer, a blocking layer, an adhesive layer, a charge generating layer, a charge transport layer and a conductive ground strip layer adjacent to one edge of the imaging layers. This photoreceptor may also comprise additional layers such as an anti-curl layer and an optional overcoating layer.
Ionographic charge receivers are designed to be contacted with streams of ions from a source (e.g. corona, stylus, ionographic head, etc.) to form a charge pattern on the receiver which can subsequently be developed. Ionographic charge receivers generally comprise two layers, an inner electrically conductive layer and an outer dielectric layer. Ionographic charge receivers are typically made by coating dielectric material on a substrate made of a metal or alloy or a substrate having a conductive coating.
Back-side erasure of imaging members in electrostatographic devices may be desirable for a number of reasons. For example, erasure mechanisms located internal to an imaging belt for providing back-side erasure minimize the size requirements in electrostatographic devices. Also, back-side erasure devices located on an opposite side of an imaging belt in relation to imaging mechanisms reduce the overall complexity of an electrostatographic device and allow easy access to the individual components of the device.
Transparent imaging members are currently being developed. Conductive layers (ground planes) comprising cuprous iodide and other I-VII semiconductors such as CuBr, CuCl and the corresponding silver salts provide desirable conductive properties while maintaining the requisite transparency desired in such members. The I-VII semiconductors are a class of compounds formed from Group IB and Group VII elements of the Periodic Table. See, for example, a review article by A. Goldmann, "Band Structure and Optical Properties of Tetrahedrally Coordinated Cu- and Ag- Halides", Phys. Stat. Sol. (b) 81, 9-47(1977).
Generally, vacuum evaporation has only been used to produce semi-transparent coatings such as the semi-transparent Al or Ti coatings used for certain photoreceptor applications. Sputtering can be used to produce conductive transparent coatings of NESA (SnO.sub.2) or ITO (In.sub.2 O.sub.3 /SnO.sub.2), but sputtering is a very slow process with very low throughput. Vacuum evaporation of these compounds generally results in a reduced material which is conductive but not transparent. Extended high temperature post deposition oxidation (e.g., 400.degree. C., 15 min.) treatment must be carried out to oxidize the evaporated material and thereby render it transparent.
U.S. Pat. No. 4,485,161 discloses an electrophotographic element comprising a conductive layer, a barrier layer and a photoconductive layer, all three of which can be coated by a variety of coating techniques such as spray coating, swirl coating, vacuum deposition, extrusion hopper coating, hand coating and air knife coating. The disclosure of the preparation of a conductive layer is limited. The patent states that the conductive layer is usually coated on a support and allowed to dry before a barrier layer is applied. A number of patents are referred to at column 7 regarding the conductive layer. These patents disclose solution coating techniques for applying a coating to a substrate. In each patent, a method is disclosed wherein a solution is applied to a substrate and the solvent is evaporated to form a film coating on the substrate. The examples of U.S. Pat. No. 4,485,161 refer to use of a polyester support which has previously been coated with a conductive layer of cuprous iodide.
U.S. Pat. No. 4,661,428 discloses at column 4 an electrically conductive substrate which may be a plate or cylindrical body made of a conductive metal whose volume resistivity is 1010 ohm-centimeter or less such as Al, Cu, Pb or the like, a plate or cylindrical body made of a metal oxide such as SnO.sub.2, In.sub.2 O.sub.3, CuI, CrO.sub.2 or the like, or a plastic film, paper, cloth or the like on which said metal or metal oxide has been coated by vapor deposition or sputtering. The examples all use a 0.2 mm thick aluminum plate as the conductive substrate.
U.S. Pat. No. 3,871,972 describes an electrorecording sheet in which an electroconductive white or light yellow layer of cuprous iodide may be vacuum evaporated or solution coated onto a color forming layer containing a component which shows visual color change or color formation due to electrochemical reaction or heat energy when current is passed therethrough. When current is applied to the color forming layer through the electroconductive layer, selective visible recording is obtained in the current applied area of the color forming layer. While thickness of the electroconductive layer was not emphasized, Examples 3 and 4 describe solution coating of the electroconductive layer to a thickness of 15 micrometers.
Conductive coatings containing copper iodide have previously been prepared by dispersing CuI in a binder and casting a film from a non-aqueous solvent; U.S. Pat. No. 3,245,833 discloses such a preparation. There are problems, however, associated with this procedure. Examples of solvents used in such preparation include nitriles such as acetonitrile, propionitrile and butyronitrile. The solubility of CuI in these solvents is low and extensive filtration is required to remove particulates. Even after filtration, particulates grow in the solutions which lead to microscopic nonuniformities in films so produced. As a precaution, mixing and filtration is carried out in the dark because copper iodide is light sensitive. Oxidation of Cu(I) to Cu(II) is a problem since the latter form is nonconducting. Additionally, a drying step is necessary to remove solvent from such films.
U.S. Pat. No. 3,677,816 discloses a conductive, transparent CuI film formed by contacting an evaporated Cu film with an iodine containing solution. The resultant thin layer of copper iodide has a surface resistivity of 5.times.10.sup.3 to 10.sup.6 ohms/L.quadrature. and a white light transmittance of 80% to 95%. Reference is made to prior art in which a cuprous iodide layer is formed by exposing a substrate surface to an atmosphere of copper vapor and then exposing the resulting copper coated surface to iodine vapor. This process is said to be disadvantageous in view of the extreme toxicity of iodine vapor, insufficient uniformity and insufficient adhesion. At col. 5, a method of producing a three-layered transparent film from an iodine containing solution is disclosed. The film has a top layer consisting of an organic photoconductive substance bonded together with a binder resin.
U.S. Pat. No. 3,505,131 describes a process for the preparation of clear, transparent cuprous iodide film for an electrostatic imaging system, comprising evaporating copper onto a substrate in the absence of substantially all oxygen and water to form a copper film, removing any oxide on the film by contact with a deoxidizer, removing the deoxidizer, and exposing the film to an iodine-hydrophobic solvent solution. Mechanical thicknesses greater than about 0.1 micrometer (optical thicknesses of over 0.2 micrometer) are disclosed.
U.S. Pat. No. 3,898,672 describes an electrosensitive recording member which works by sparking between a stylus and a recording electrode. The member is comprised of CuI, an electrically reducible metal compound, and an organic binder. A thickness of 5 to 100 micrometers is disclosed.
U.S. Pat. No. 3,905,876 discloses an electrorecording sheet in which the conductivity of a solution coated CuI layer is enhanced by increasing the iodine content relative to Cu by 0.05-0.2% by weight. The increase in iodine content can be effected by removing Cu+ ions by treatment with the oxidizing agent potassium permanganate. A small quantity of KMnO.sub.4 is simply milled with the CuI powder. In this process some Cu+ is transformed to Cu2+ and some Cu+ is correspondingly liberated. The excess holes give enhanced p-type conductivity. To add excess iodine, materials such as iodoform are added to the milling mixture.
U.S. Pat. No. 4,133,933 discloses an electrorecording sheet with improved whiteness in the sheet which comprises precipitated cuprous iodide.
U.S. Pat. No. 3,661,648 describes a method for preparing electrochemical cell electrodes comprising providing a metallic copper containing carrier body, providing a concentrated non-aqueous solution of cupric chloride in organic solvent, and immersing the metallic copper carrier into said solution at ambient temperature. The resulting corrosive action of the cupric chloride on the metallic copper provides corrosive conversion of part of the copper metal of the carrier into cuprous chloride. The remaining unconverted metallic copper of the carrier serves as a conductive current carrier for the electrode.
U.S. Pat. No. 4,069,356 describes a method for forming photoconductive layers of chalcogenides of Cd or Zn with high photoconductivity gain. To provide high photoconductivity gain the material is typically doped with a metal (usually copper) and a halogen (usually chlorine). The method consists of forming a pellet from mixed powders of the chalcogenide and a small amount of copper halide, preferably between about 0.1% and 2.0% by weight of the total mixture. The pellet is then vacuum evaporated onto a substrate, typically to a thickness of 1-5 micrometers, and baked in an oxygen rich atmosphere. The baking allows diffusion of the halide donor and copper acceptor dopants into the crystal.
U.S. Pat. No. 4,284,699 discloses an electrical conducting support, for example, aluminum paper laminates; metal foils; metal plates; vacuum deposited metal layers such as silver, nickel, chromium, aluminum and the like coated on paper or conventional photographic film base such as cellulose acetate, polystyrene, polyethylene terephthalate; etc. Such conducting materials as nickel can be vacuum deposited on transparent film supports in sufficiently thin layers to allow electrophotographic layers prepared therefrom to be exposed through the transparent film support if so desired. Example 5 refers to a conductive layer of copper iodide.
U.S. Pat. No. 4,758,486 discloses an electrophotographic photoconductor comprising an electroconductive layer made of aluminum deposited on a support material by vacuum evaporation.
U.S. Pat. No. 3,428,451 discloses radiation sensitive recording elements comprising a conductive layer and a recording layer. The conductive layer may comprise cuprous iodide or another semiconductor compound dispersed in a resin binder.
U.S. Pat. No. 4,350,748 discloses a process of manufacturing printing forms or printed circuits by coating an electrically conductive support with an organic photoconductive layer. The materials to be coated may comprise metals such as aluminum, copper, zinc or magnesium or metal compounds such as aluminum oxide, zinc oxide, indium oxide or copper iodide. In one example, a film on which aluminum has been vapor deposited is used to transfer photoconductive material onto an aluminum plate.
Conductive substrates used previously for electrostatographic applications lack oxidative stability. A need therefore exists for an oxidatively stable conductive substrate for electrostatographic applications.